I'm not really interested in his personal life,
In all seriousness, perhaps Cruise's interest in sci-fi is related to his beliefs in Scientology and that -sci fi plays much into their belief system related to Xenu and the end of civilization?
Just a guess.
Regarding his stature in modern sci-fi - I'm not sure he's any bigger than Zoe Saldana, Harrison Ford, or Bruce Willis. And with SW coming up - and if Fisher, Hamill and Ford possibly showing up again - that will eclipse everything else out there.